The throughput of a closed loop controlled feeder is computed from the weight of the conveying system, including the hopper containing the material to be fed, which varies with time. As the hopper empties there is a "loss-in-weight". For this purpose the weight of the system is sampled at well defined instances and the sampled signal is differentiated to produce a throughput signal which is proportional to the throughput. The throughput may vary with time because the bulk material density may vary with time. The just mentioned throughput signal contains signal components which are caused by disturbances of the signal sensor or sampler. Such sensor disturbances or faults called observation noise in this disclosure, can be caused by several different sources, for example, by accelerations at the location of the weighing system, by electrical noise, or by so-called quantization noise. On the other hand, bulk material density variations constitute disturbances which, for example, can be caused by such factors as lumpy bulk materials or by a non-uniform supply of the bulk material to the feeder. Such disturbances cannot be predicted in time. Therefore, these disturbances are generally referred to as stochastic noise. Further, the above mentioned observation noise cannot be separated from the wanted signal of the weighing system, and therefore, these disturbances also falsify the feeding result.
German Patent Publication (DE-OS) 3,721,186, based on U.S. Ser. No. 879,430, filed on Jun. 27, 1986now U.S. Pat. No. 4,775,949, discloses a closed loop controlled feeder in which observation noise and bulk material density variations are taken into account by way of a model calculation, whereby the size of these disturbances and variations are taken into account when an estimated value is formed. In the known system a Kalman filter process is used to estimate the actual weight and the throughput or feed rate of the material. The estimated throughput signal is produced based on a model of the known feeding and weighing system, on the measured weight, and based on stochastic models for the noise phenomena that influence the system. The models for the different types of noise are modified in accordance with the size of their influence on the system and in accordance with the probability of their occurrence. In the known method the observation noises are taken into account in that prior to placing the particular feeding system in service, the variance .rho..sup.2.sub.n serving for the calculation of the model must be ascertained either experimentally or empirically. Such a system or method has the disadvantage that the mathematical model can be calculated only with the aid of the characteristic values of the particular system that have been ascertained experimentally or empirically prior to putting the system into actual use. The characteristic values so obtained have no application of a general nature and in general cannot be used for other systems.